Radio transmitting system



I Oct. 16, 1928.

.1 ,687,896 F. M. RYAN RADIO TRANSMITTING SYSTEM Filed April 5, 1924 F/QZ Z6 :7 a/ ,7 I 30 33 I30 a i \52 ER 6% M 221m- Z E 1k Mada/army Appahvfms Amp/mar AAA /nvenf0n (mm/3 M- Ryan by y to 12,, 1 sa e i. wet, lo, who.

, UNITED STATES PATENT. OFFICE.

FRANCIS M. RYAN, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OE NEW YORK, Y., A CORPORATION OF NEW YORK.

RADIO TRANSMITTING SYSTEM. i

Application filed April 5,

This invention relates to a radio transmit-. ting system ant. more particularly to means whereby an apparatusfor supplying high fre quency energy may be coupled to an antenna circuit.

The operation of three electrode space discharge devices, especially at high efficiency, is attended by a distortion of the transmitted wave so that the external output circuit associated with the devices is supplied with,'besides the components to be repeated, other undesired components produced by the operation of the devices. These undesired components may be harmonics of the wave to be repeated.

In radio systems includingdischarge devices of the type described above operating at high efficiency, it has been found that undesired oscillations of considerable amplitudes are produced and are radiated. In some cases the harmonic frequency energies transmitted have been of such large amplitudes that, because of interference with the nearby stations, the interfering station has been forced to suspend operations,

The present invention provides an arrangement whereby high frequency apparatus, in-v cluding three-electrode space. discharge devices operating at hi h etliciency, may; be. coupled. to an antenna circuit so that substantially all of theenergy radiated from the antenna is of selected frequency. I

According to the present invention radio tranemitting apparatus embodying three electrode space discharge devices, is coupled to an circuit by means of a tuning unit provided with relatively large capacity condenser for transferring energy of desired frequency to the antenna, while substantially excluding waves of other high frequencies.

Gnc object of this invention is to so couple a source producing energy of different high f piencies to an antenna circuit that energy of desired frequency produced by the source may be selected and radiated from the an tenna.

A feature of this invention relates to a unit com 'irisiug a condenser of relatively large capacity for coupling, in energy-transfer relation, a source producing waves of different frequencies and an antenna circuit so that waves of desired frequency only may be transmitted from the antenna.

For a complete understanding of the in- 1924 Serial No. 704,332.

vention and the operation of its different parts reference may be made to the following description read in conjunction with the attached drawing in which Figs. 1, 2 and 3 illustrate radio transmitting arrangements embodying the invention. 7

In Fig. 1 isshown a radio telephonesystem. Speech or other low frequency signal currents are su plied by the circuit 1, which maybe a telephone line, to the modulating apparatus 2. This apparatus may embody any well known system for producing-a modulated carrier wave. For example, the low. frequency waves from the circuit'l and a carrier wave produced by a separate source may be supplied to and combined in a modulator,

. as dlsclosed in United States Patent 1,245,446,

November 6, 1917 to England; or the low frequency waves may be supplied to an apparatus which also functions to modulate a carrier wave generated by the apparatus, as disclosed in Patent 1,442,147, January 16, 1923 to 'Heising. i

The modulated waves are'transmitted by the transformer. 3 .to an amplifier 4, hereinshown as a three-electrode space discharge.

device. A source 5 supplies polarizing potential to the impedance control electrode of the amplifier, whereby this device may be caused to operate upon the lower curved portion of its input-voltageoutput-current characteristic curve thereby resulting in highly eii icientoperationof the amplifier.

Space current is supplied by the source 6 through the choke coil 7 which functions to prevent the high frequency wavesfrom being short circuitedthrough the source 6. The alternating current output circuit path extends from the anode through the blocking condenser 8, to the tuned'circuit, comprising I transferring energy from the amplifier to the Condenser 8 is adapted to prevent short plifier 4. This voltage is also impressed upon the path including the condenser 8, inductance 9 and condenser 11 shunted by the coil 12. The direct current potential across this path, in the absence of the coil 12, would divide in the direct ratio of the resistances of the condensers 8 and 11 and hence would re quire that the condenser 11 be designed to withstand high voltages. A condenser of large capacity adapted to withstand high voltages is both bulky in construction and expensive to manufacture. By using a coil 12 of high inductance and low resistance, in shunt to the condenser 11, the direct current potential supplied by the source 6 is caused to be largely concentrated upon the relatively low capacity and inexpensive condenser 8, while the desired value of high frequency voltage will be effective across the condenser 11;

The coil 12 is also included in the antenna circuit and is adapted to operate as a leak path to ground, about'the condenser 11, for static charges incident upon the antenna 13.

Because of the distorting action of the three-electrode space discharge device, when used as a high efiiciency amplifier, there will be produced in the output circuit undesired oscillatory impulses harmonically related to the frequency of the waves impressed upon its input electrodes. 4

These harmonically related impulses togethcr with the amplified modulated waves of fundamental frequency will be supplied to the tuned circuit. By selecting the proper relative capacity values for the condensers 10 and 11, i. e., by making the capacity of condenser 10 small compared with the capacity of condenser 11, the voltages of the different frequency waves impressed upon the condenser 10 may be made large compared to the voltage drop across the condenser 11.

The antenna circuit is resonant to the frequency of the modulated waves of the fundamental. frequency. Because of this fact waves of this frequency will be readily transferred to the antenna and their amplitudes will be large, whereas the amplitudes of the oscillations of undesired frequencies will. be sharply attenuated and hence will be reduced to a negligible value.

Referring now to Fig. 2 there is shown a radio telegraph system including a space discharge oscillator comprising two three-electrode devices 15 and 16 associated with a single oscillating or frequency determining circuit 17.

A single phase alternating current source 18 supplies energizing current to the devices 15 and 16 through the transformers 19, 20 and 21.. v

point of the secondary winding and to ground by the conductor 23. The condensers 22 are provided for a purpose to be referred to here- I inafter.

Space current is supplied to the devices 15 and 16 from the source 18 through the transformer 21. The terminals of the secondary winding of the transformer 21are connected to anodes of the discharge devices 15 and 16 through the coils 24 and 25 respectively, while its midpoint is connected to the conductor 23 and hence to the filaments of the two dis charge devices.

The space current path for the device 15 maybe traced as follows: from the lefthand terminal of thesecondary winding of transformer 21, through the coil 24 to its anode and across the space Within the deviceto its cathode, through both halves of the secondary winding of the transformer 19 and conductor 23 to the midpoint of the secondary of trans former 21. f

The space current path for the device 16 extends from the right handterminal of the secondary of transformer 21, through the coil 25, the anode of 16, across the space within the device to its cathode, through both halves of the secondary winding of the transformer 20, and conductor 23 to the midpoint of the secondary of transformer 21.

With this arrangement one half cycle of the alternating currentwill be transmitted vice 15 and the other half cycle will be supplied through the coil 25 to the space path of the device 16. The coils 24 and 25-offer high impedance to radio frequency currents preventing short circuiting by the transformer 21. r

The oscillating or frequency determining circuit 17 comprises the adjustable inductance 26 and condensers 27, 28 and 29. The periodicity of this circuit may be controlled, and hence the frequency of the oscillations generated may be regulated by varying the induct-.

ance 26.

The alternating current output path of the devices 15 and 16 extends from their anodes through the blocking condensers 30, the adjustable contact 31 associatedwith the in-- duct-ance 26, the oscillating circuit 17, conductors 32 and 23, condensers 22, to the cathodes of the devices 15 and 16, and across the spaces within them to their anodes.

The input circuits extend from the cathodes of the devices across the spaces within them to their grids and thence via conductor 33,

lill

condenser 29and conductors 32 and 23, back to the point of beginning.

The condenser 29 functions to feed incre-' ments of energyproduced in'the oscillating circuit 1? to the grids or" the devices .15 and 16 for controlling the iiow of current across the space paths witl n, them whereby, as is well known, sustained oscillations of the frequency determinedby the constants of the circuit 17 are generated. Condensers 22 serve as low impedance, paths; in shunt to the secondary windings of the transformers 19 and 20, for theoscillations generated.

The grids of the devices and 16 are connected to their cathodes by a leak path comprising the inductance 34 and resistance 35. Except for the fact that the devices 15 and 16 serve to rectify-both halt waves of the alternating current supplied by the source 18, the oscillator described above is identical with that disclosed in U. S. Patent 1,624,537, April 12. 1927. to Colpitts.

.circuit is of relatively large capacity compared with that of condensers 27 and antenna 36. V I

Because o'l 'the distorting action of the space discharge devices, there will be generated in addition to oscillations of the frequency determined. by the :circuit 17 other high frequency oscillations. The amplitudes oi? the higher frequency oscillations will be largely determined by the degree of coupling which exists between the input and output circuits of the discharge devices, due not only to the condenser 29, but to the inherent'reaetances of the circuits ofthe oscillating system. V

. These reactances may comprise the internal capacities between the electrodes of the devices 15 and 16 and the inductance and capacity eli eets of the iead in wires and external conductors associated with the oscill ng devices. p v

7 As inv the arrangement previously described the ca Jacity values of the condensers included in the oscillating circuit are so chosen that the potentials developed across the coupling condenser 28 by the waves of dii l'crent high tre-. quencies ES small compared to the voltage drop across the condenser 27. The antenna circuit being resonant to the wavs of funda mental frequency, the amplitudes of waves of this frequency supplied thereto and radiated will be large, while those of the higher trequeucies will be negligible.

The waves generated be controlled in accordance with code signals erated. This oscillating circuit includes 13110 and a small capacity condenser 51.

by the oscillatorrnay in any well known manner,-for example,a

key 38 may be included in the primary circuit of the transformer 21. In Fig. 3 there is shown a radio telephone system which is slightly different from that shown in Fig. 1. Speech or other low frequency signal currents.- such as music or other matter constituting a programme to be transmitted, is supplied by the circuit 36, amplified by the device 37 and impressed upon the input circuit ofa modulator 38*; Space current is supplied to the modulator by the source 39. The negative terminal of the source 39 is connected to the cathode of the modulator through a resistance 40. The volt.- age drop across the resistance 40 is impressed upon the impedance control electrode of the modulator 38, to provide normal grid polarizing potential. r l 1 Th'esource 39 supplies space current to the modulator and the electric discharge device 41 of the associated oscillator through a high impedance choke coil 42. The lead connect-.

the coil 44 shunted by'the adjustable condenser 45 and the blocking condenser to its cathode, and across the'space within, the device to its anode.

The inputcircuit of device 41 may be traced from the cathode through the leak Sll path 46, consisting of a condenser shunted by a resistance, and coil 47 to its control elec trode, and across the space path within the device to its cathode. l

The output and input circuits of the device '41 are coupled in feed back relation bythe closed oscillating circuit which substantially determines the' frequency of the oscillations genvariometer, comprising the series connected coils 48, 49 and 50, a coupling condenser52, I Coil 48 is inductively associated withthe output coil 44 and is fixed, as isa-lso coil 50, inductively associated with the input coil 47, while coil 49 is carried by an element which is movable relatively to coils 48 and 50. lVith this arrangement theinductance of the unit and hence the frequency of the oscillations pro duced may be varied.

The antenna circuit comprising the aerial 53 is connected to 'roundthrough variable tuning inductance 54 in series with the coupling condensr-ir 52. A high re constituting a static leak path, is connected between the aerial and ground in. parallel with the coil 54and condenser 52.

The transmitter just dcscribml operates on the constant current principle disclosed in Ill! . United States Patent 1,442,147, January 16,

1923, to Heising. Briefly described the low frequency signal waves supplied by the circuit 36 are amplified by the device 37 and plied to the control electrode of the modulator. Variations in the amplified current supplied to the input circuit of the modulator 38 will produce a like variation in the utput circuit of the device ll of the elated oscillator, so that the voltage supplied to the oscillator will he mod dated in accordance with the low frequency signal WELVBS.

Because of the'distortinp; action of the device 11 and the inherent reactances of the circuits associated with it, there will be supplied. to the frequency determining circuit oscillations of undesired frequencies.

The capachy values of the condensers 51 and 52 included in the oscillating); circuit are so chosen that the high frequency potentials developed across the condenser 51 large, and those across the condenser 52 are relative ly small. mental frequency of the n'iodulated waves.

As described above, because of the discriminatory effect of the antenna circuit in cooperation with the coupling condenser, the amplitude of the fundamental frequency modulated wave supplied to the antenna and radiated therefrom will be l. ;e while tl {1 higher frequency oscillations will be sharply attenuated and hence the amplitudes of the energy of undesired frequencies radiated will be practically negligible.

Arrancjements including the tuning" unit describedabove have been tested. During;- these tests, oscillations of undesired frequencies of considerable amplitudes were present in the oscillating circuit, it was found that the energy of the undesired frequencies radiated from the antenna circuit was negligible.

In one case an apparatusofthis type which was tested included a high efiiciency threeelectrode discharge device supplied with space current at 10,000 volts and transmitted upwards of one kilowatt at about 610,000 cycles to an antenna through an oscillating circuit having; a tuning condenser of .00075 Mv F. capacity and a coupling condenser of .01. M. F. capacity. Nhile harmonics of considerable strength were readily detected in the oscillating circuit, the field strength-of the harmonic oscillations a fevvvmiles from the transmitting; station as compared with that of the fundamental frequency was apn'atcly as 1 to 1000 and hence the energy as 1 to 1,000,000.

In another arrangement, including a threeelectrode discharge device supplied with space current at 10.000 volts and transmitting upwards of six kilowatts to the antenna at approximately 210,000 cycles, harmonics of relatively large amplitudes were present in the oscillating circuit which included a tuning condenser of .002 mmf. capacity and a The antenna is tuned to the fundacoupling condenser of .05'mf. capacity, but it was lmpossible to detect any'harmonics in the antenna circuit.

discharge device operating at high efficiency, I

whereby energy of selected frequency and at relatively high voltages may be rad ated from the antenna to the exclusion of energy 7 of other frequencies.

While certain arrangements and specific details have been described for the purpose of clearly and completely disclosing the nature of'the invention it is to be understood that this invention is not to be limited thereto but only by the scope of the attached claims.

What is claimed is: I

1. In combination, an antenna circuit tuned to the frequency of the wave to be radiated, a closed oscillatory circuit tuned to theatrequency of the oscillations to be radiated by said antenna, said circuit including two series capacity elements of widely differing maflnitudes the laro'er ca )acit element bein t: o t

commonto said oscillatory. circuit and said" antenna circuit, and means for, producing and transferring to said oscillatory circuit continuous oscillations of the frequency to be radiated comprising a space discharge device having a cathode,an anode and a grid, input and output circuits therefor coupled by said oscillatory circuit, whereby oscilla tions of the frequency to be radiated'are readily transferred to said antenna circuit to the substantial exclusion of oscillations of higher frequencies. l l

2. In combination, an antenna circuit tuned to the frequency of the wave to be radiated, a closed oscillatory circuit tuned to the frequency of oscillations to be radiated by said antenna, sald circu t lIlOlllCllIlQ, two series capacity elements of widely differing magni tude the larger capacity element being common to said oscillatory circuit and said an tenna circuit, and a space discharge device having a cathode, an anode and a grid, input and output circuits therefor conductively coupled to said oscillatory circuit to supply thereto continuous oscillations of the fre quency .tobe radiated, whereby oscillations of the fundamental frequency to be radiated are readily transferred tosaid antenna circuit-to the substantial exclusion of oscillations of higher frequencies. r

In witness whereof, I hereunto subscribe my name this first day of April, A. D. 1924i.

FRANCIS M. RYAN. 

